The present invention relates to a hydrophilic polymer of a block copolymer and/or a graft copolymer having special binding system of a hydrophobic hard segment and a hydrophilic segment having a hydrophilic group connected to thioether bond on a side chain and a process for producing the same. More particularly, it relates to novel hydrophilic polymers which have excellent water swelling property and water absorbing property and are useful as a water repellent, a water retainer, an antistatic agent, a perspiration absorber an antidewer, etc.
The conventional water insoluble hydrophilic polymers such as water swellable polymers and water absorbing polymers include
(1) water insoluble polymers produced by modifying polyethyleneglycol (PEG),
(2) polymers produced by crosslinking water soluble hydrophilic random copolymers or homopolymers by various methods in sigma bond to be water insoluble and if necessary, further chelating the water insoluble polymers, and
(3) polymers produced by grafting acrylonitrile on starch, if necessary, further hydrolyzing the graft copolymer.
These hydrophilic polymers are useful as an anti-water-leakage, a water retainer, an antidewer, an antistatic agent, a cement reinforcing agent, a perspiration absorber etc.
These hydrophilic polymers have been studied for each usage. It has not been known to provide a hydrophilic polymer having high water swelling degree and water swelling force and high gel stability in preservation which can be controlled as desired.
The polymers (1)(modified PEG) have high water swelling degree but have low water swelling force which is remarkably decreased by an addition of a material having high cohesive force. Accordingly, the purpose could not be attained.
In the polymers (2), the water swelling degree is dependent upon the degree of hydrophilic groups and the crosslinking degree which are contradictory each other. The crosslinkage is chemically stable sigma bond, whereby it is not easy to treat in a post-treatment or to disperse it in a medium.
The polymer (3) of acrylonitrile grafted starch or its hydrolyzed ones have high water absorption for absorbing 50 times of water to polymer, however the polymers are perishable in storage and decompose their gel structure.